1. Field of The Invention
The present invention relates generally to an artificial blood vessel composed of a tubular body made of fibers. More specifically, the invention relates to an artificial blood vessel which has properties approximating those of a vital blood vessel so that the tissue of endothelial cells can excellently adhere thereto.
2. Description of The Prior Art
In recent years, artificial blood vessels composed of a knitted or woven fabric made of polyesters, such as polyethylene terephthalate, and composed of an oriented polytetrafluoroethylene, have been developed and widely used. However, these artificial blood vessels are solid and do not have sufficient elastic properties so that their physical properties are unlike those of a vital blood vessel. Therefore, there is the disadvantage in that they are difficult to suture to a vital blood vessel. In particular, there is the disadvantage in that an artificial blood vessel made of a polyester cloth easily causes so-called kinking.
In order to eliminate the aforementioned disadvantage, crimp processing has been carried out to improve the bending and pressing resistances of an artificial blood vessel. In this case, there is another disadvantage that the inner surface (the bloodstream surface) of the artificial blood vessel is not smooth.
In recent years, small-diameter artificial blood vessels which can be used in the transplant into a peripheral arteria have been developed. Such a small-diameter artificial blood vessel must have a smooth and flat inner surface to have sufficient antithrombogenicity. Such a small-diameter artificial blood vessel is often made of a porous elastomer. However, when the aforementioned artificial blood vessel is made of the cloth, if crimping is carried out to improve the bending and pressing resistances of the artificial blood vessel and thereby prevent kinking, it is difficult for the artificial blood vessel to have the smooth and flat inner surface necessary for sufficient antithrombogenicity.
Furthermore, the aforementioned small-diameter artificial blood vessel preferably has a patency similar to the physical properties of a vital blood vessel to maintain the uniformity of the bloodstream. It has been reported that a difference between the physical properties (the elastic properties) of a vital blood vessel and an artificial blood vessel causes a disturbance of the bloodstream, and particularly that thrombus easily occurs at the anastomosed portion between blood vessels having different physical properties. Therefore, the raised intima influences the patency of the artificial blood vessel in long-term use (Kinley CE et al.; Compliance: a continuing problem with vascular grafts.; J Cardiovas Surg 21, 163-170 (1980)). It has been also reported that in order to solve the aforementioned problem, an artificial blood vessel must have physical properties (elastic properties) approximate to those of a vital blood vessel (Waden R. et al.; Marched Elastic Properties and Successful Arterial Grafting, Arch Surg vol. 115, 1166-1169 (October 1980)).
In order to solve the aforementioned problem, various artificial blood vessels made of elastic materials with physical properties similar to those of a vital blood vessel, have been developed. For example, such artificial blood vessels are composed of an elastic polymer of porous polyurethane (JP-A-60-182958 and JP-A-60-188164), a multi-layer porous structure for preventing static electricity (JP-B-62-11861), and a laminate of non-woven porous sheets (JP-A-62-183757).
It has been recently reported that an artificial blood vessel made of polyurethane easily degrades after a long-term implantation (Tahara et al.; Clinical and experimental study on the insulation damage of polyurethane pacemaker leades: Jpn J Artif Organs 19(4), 1427-1431 (1990)). Therefore, it is preferable that an artificial blood vessel is not made of polyurethane. Furthermore, it is known that an artificial blood vessel is an artificial organ which is to be permanently operated in an organism, and water hammer stress due to strongly pulsing bloodstream is applied to the artificial blood vessel. Therefore, degradation of the material causes aneurysm, which must be prevented.
Furthermore, in the case of a small-diameter artificial blood vessel of a cloth, the aforementioned crimp processing should not be carried out in order to prevent an increase in thrombus.